Re: Sharing memory between user and kernel spaces [Re: copy_to/from_user and a bottom half]

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Alex Ivchenko <aivchenko@ueidaq.com> wrote:
> 4. Then one can translate kernel-space virtual address into physical
> one to supply to scater-gather BM-capable hardware.
>
> Is it any way to do this with Linux?

   For 2.2.x kernels, look at the rvmalloc/rvfree functions in
linux/drivers/char/bttv.c I would recommend overriding your
driver's mmap method to allocate memory (via rvmalloc) that
can be used in both user and kernel space. As a bonus, such
allocated memory is usable in interrupt contexts. However, it
is NOT contiguous pages (since it's based off of vmalloc) and
can't be used for linear DMA (scatter-gather should work fine, though)

        On 2.3.x kernels, I hear that the kiovec() routines are
the way to go for this kind of I/O, but I haven't tried them out
myself.

-- 
Jason McMullan, Senior Linux Consultant, Linuxcare, Inc.
412.422.8077 tel, 412.656.3519 cell, 415.701.0792 fax
jmcmullan@linuxcare.com, http://www.linuxcare.com/
Linuxcare. Support for the revolution.
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